The invention relates to an apparatus for treating ion-exchange exchange resin from a nuclear plant in which a mill is provided for comminuting the ion-exchange resin. An apparatus of that type is disclosed, for example, by U.S. Pat. No. 5,564,103.
In a nuclear plant, in particular in a nuclear power plant, wastewater streams or condensate streams are customarily subjected to purification.
In this type of purification, in particular for final purification, ion-exchange resins can be used in bed form (e.g. mixed bed filter) or in the form of precoat layers, especially for deionizing the respective wastewater stream or condensate stream. Depending on the ion type occurring, anionic and/or cationic ion-exchange resins can be used. The respective ion-exchange resin can be used in powder form as powder resin. Alternatively, ion-exchange resin can also be used in the form of small beads (bead resin).
After use, the ion-exchange resins used as purification material or filter material are transferred to a final storage. Fine-grained or pulverulent ion-exchange resins can be subjected here to a chemical or thermal treatment which reduces their swelling capacity. After such reduction of the swelling capacity of the respective ion-exchange resin, incorporation of the ion-exchange resin into a cement matrix or bitumen matrix is feasible, without the matrix being destroyed by swelling of the ion-exchange resins. A pulverulent ion-exchange resin is particularly suitable for final storage in this manner.
In contrast, in the case of a coarse-grained ion-exchange resin or in the case of a bead resin, only a limited reduction in the swelling capacity is achievable by a chemical or thermal treatment. Size reduction or comminution of coarse-grained or bead form ion exchange resin has therefore been desired but found to be difficult in practice, at least in part because the consistency of the resin particles is tough, gummy, a bit clammy. Therefore the particles cannot be ground like grain but have to be torn into pieces. Robust and long lasting apparatus to do this has not been-available. Therefore, these ion-exchange resins are customarily stored temporarily or finally in dewatered or dried form or using a binder. However, in this type of storage, undesirable swelling and thus damage to the ion-exchange resin packaging is still possible in the event of water ingress.
It is accordingly an object of the invention to provide an apparatus for treating ion-exchange resin which overcomes the above-mentioned disadvantages and makes possible particularly reliable temporary storage or final storage even of coarse-grained ion-exchange resin or of bead resin.
It is a further object of the invention to provide for the incorporation into a cement matrix or bitumen matrix of coarse-grained ion-exchange resin or bead resin by suitable reduction of the swelling capacity of the ion-exchange resin or of the bead resin in a similar manner to the treatment of a fine-grained ion-exchange resin. In order to make possible such a reduction in the swelling capacity of the coarse-grained ion-exchange resin or of the bead resin, the coarse-grained ion-exchange resin or the bead resin should first be comminuted in the manner of a pretreatment.
It is also an object of the invention to provide for this purpose a suitable comminution apparatus.
With the foregoing and other objects in view, there is provided according to the invention an apparatus for treating ion-exchange resin from a nuclear plant in which a mill is provided for comminuting the ion-exchange resin in which the mill is a disk mill having as grinding elements a plurality of disks including corundum.
The comminution apparatus provided is a disk mill which has as grinding elements a number of disks including corundum. In this case, the grinding elements provided are at least one stationary stator disk including corundum and at least one rotor disk including corundum which rotates relative to a stator disk. A rotor disk is preferably a horizontally rotating disk so that the particles to be torn do not fall off too easily.
In an adjustable gap provided between the stator disk and the rotor disk, the comminution of the ion-exchange resin can be performed by shear forces and cutting forces. In particular, due to the physical properties of the ion-exchange resin, that is to say due to its elasticity, the use of a disk mill with disks including corundum has proved to be particularly effective in the comminution of the ion-exchange resin.
The purpose of the mill is to tear the tough and gummy ion-exchange-particles apart. Therefore the disks in the mill have a very rough surface with corundum particles on the surface having sharp, cutting, tapering edges and points which grip the ion exchange resin particles and tear and cut them apart. Thus, the process in the disk mill with disks including corundum is not a grinding process but rather a cutting and tearing process.
For that reason the hardness of the surface of the disks is not the most relevant. The following properties are more important:
1. The surface of the disks including corundum has to be rough. The corundum surface is like sand paper, where sand or sanding particles are glued on a solid base material. The remainder of the disk can be corundum or any other suitable base material.
2a. The particles of the surface have to be rather large, with a diameter of about 1 mm to 2 mm. That means that the particles have to be made from a material which affords very firm, strong, non-brittle particles of that size. Silicon carbide for example is extremely hard, but silicon carbide particles are smaller, are not available in that large size and tend to break in the milling process. Corundum particles, in contrast, suit perfectly for robust large particles.
2b. A second reason for large corundum particles is that otherwise disks would be easily gummed up and covered with the tough and gummy ion exchange resin particles. With a smooth surface this is easily the case.
3. The particles should have sharp and cutting edges and points. Broken corundum has such edges and points naturally. It is like broken glass, only harder and tougher.
Accordingly, any material with the above described properties can be taken for being glued on the disks of the disk mill according to this invention. Corundum has these properties, is common, cheap and easy to handle.
Disks including corundum having the mentioned properties are commercially available, as well as disk mills with such disks.
In accordance with a particularly preferred feature of the invention, for a particularly reliable treatment of the ion-exchange resin, the disk mill is advantageously connected into a recirculation circuit of the ion-exchange resin. Thus repeated passage of the ion-exchange resin through the disk mill is possible, with more intensive comminution being achievable from passage to passage in particular by variation of the gap between the grinding elements of the disk mill. The ion-exchange resin is pumpable in a suspension after a first comminution and thus can be recirculated, although coarse-grained ion-exchange resin or bead resin customarily sediments.
The advantages achieved by the invention are, in particular, that by the use of a disk mill with disks including corundum in the treatment of an ion-exchange resin from a nuclear plant, comminution of the ion-exchange resin is possible using particularly measures. The comminution can be carried out in this case, in particular after a plurality of passages of the ion-exchange resin through the disk mill, up to a particle size of the ion-exchange resin of less than 200xcexc. The swelling capacity of an ion-exchange resin treated in thus manner can be reduced by means of a thermal or chemical treatment.
Ion-exchange resin formerly in bead form which has been treated in this manner can thus be fed to a particularly suitable temporary storage or final storage, for example by incorporation into a cement matrix or bitumen matrix.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in an apparatus for treating ion-exchange resin, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawing.